很好奇“ rank（）”语句中“（）”的作用以及如何应用它们。
例如，以下是标准排名查询，但我从未在关键字“ OVER”后的方括号内填充“（）”，并且很好奇它的用途是什么？
SELECT RANK() OVER (ORDER BY col1 DESC)
FROM DUAL;
答案 0 :(得分：2)
#
# Inputs.
#
x <- c(0,2,9,10,11,12,13,14,15,16,17,20) # Current scores
n <- 17 - 7 # Number of rounds left
n.flips <- 3 # Flips per round
p <- 1/2 # Chance of success per flip
#
# Derived quantities.
#
n.players <- length(x) # Number of players
m <- n.flips * n # Number of flips to go
z <- 0:m # Possible outcomes for any player
prob <- dbinom(z, n.flips, p) # Their chances
#
# Compute individual chances of wins and ties.
#
scores <- sort(unique(x))
chances <- sapply(scores, function(score)
{
j <- min(which(x == score))
y1 <- sapply(0:m, function(k)
{
exp(sum(pbinom(x[j] + k - x[(1:n.players)[-j]], m, p, log.p=TRUE)))
})
y <- sapply(0:n.flips, function(k)
{
exp(sum(pbinom(x[j] + k-1 - x[(1:n.players)[-j]], m, p, log.p=TRUE)))
})
c(Win=sum(prob * y), Tie=sum(prob * (y1-y)))
})
#
# Check with a simulation. It will do a few thousand iterations per second.
#
set.seed(17)
sim <- replicate(1e4,
{
Z <- rbinom(n.players, m, p) # The future results
final <- x + Z # The final scores
scores <- table(final) # The unique final scores
k <- length(scores)
if (scores[k]==1)
{
Win <- final == max(final) # Tally who wins
Tie <- rep(0, n.players)
}
else
{
Tie <- final == max(final) # Tally who ties
Win <- rep(0, n.players)
}
rbind(Win, Tie)
})
sim <- apply(sim, 1:2, mean) # Average over the iterations
#
# Display the results.
#
colnames(chances) <- paste(scores)
scores <- sort(unique(x))
sim <- sapply(scores, function(score) sim[, min(which(x==score))])
colnames(sim) <- paste(sort(unique(x)))
print(round(chances, 4))
print(round(sim, 4))
是一个不带参数的函数。
（通常）调用函数需要括号。它们只是表明这是一个函数调用。在这种情况下，该功能需要其余的窗口框架，因此需要RANK()。